Airbag cover and apparatus for producing an invisible tear seam therein

ABSTRACT

A cover for an air bag unit is disclosed having a patterned tear seam therein defined by an integrally bonded, thermoplastic filler strip as the cover material and comprising a material having properties different than that of the cover material, Apparatus for forming the cover includes a thin shell mold having an inner surface that is heated to melt thermoplastic material cast thereon, A powder box adapted to contain thermoplastic material therein for distribution onto the thin shell mold carries a gasket having a shape corresponding to the tear seam shape. The powder box and gasket are adapted to be connected to the thin shell mold for forming a sealed footprint on the inner surface during distribution of the cast material against heated surface portions of the thin shell mold to form a thermoplastic cover with an opening therein that have the tear seam pattern, The opening is later filled with the lesser strength thermoplastic material to form an integrally bonded thermoplastic filler strip.

This is a division of application Ser. No. 951,874, filed on Sep. 28,1992 now U.S. Pat. No. 5,288,103.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to covers for air bag units located within theinterior of a motor vehicle and in particular relates to covers having atear seam therein that is configured to define an uninterrupted outersurface on the cover. Further, the invention relates to an apparatus anda method for forming hidden tear seams in such covers for air bag units.

2. Description of the Related Art

Various proposals for covering air bag units have evolved. One primaryobjective is to provide a cover that has a weakened section therein thatwill separate upon air bag deployment to provide an opening in the coverthrough which the air bag can escape following vehicle impact that issensed by a controller. A gas generator is ignited by the controller toproduce gas for inflating the air bag as it is deployed.

Air bags are mounted in canisters that can be mounted in the steeringwheel or in an instrument panel or crash pad on the driver's side of thevehicle. If the air bag is mounted on the passenger side, typically thecanister is stowed behind an instrument panel either in a top mountposition or in a front mount position. Such mounting arrangementsrequire that the cover material of the steering wheel hub or the skin orcover of the instrument panel be specially configured during manufactureto produce a weakened section to define a seam therein that will readilyopen during bag deployment.

Such manufacturing methods and resultant structure must consider variousfunctional and aesthetic requirements. The seam must be configured toseparate such the air bag can be deployed immediately after vehicleimpact. However, the cover must have a seam that is configured such thatthe air bag unit is protected against either accidental or intentionaltampering and additionally the seam should be configured to meet longterm weathering and interior design appearance requirements. As todesign appearance, there is a desire in some cases to form the surfaceof the cover as a smooth uninterrupted surface so that there is noindication that there is an air bag unit disposed beneath the surface.This interior design objective is desired both from a human psychologystandpoint and from a pure esthetics standpoint. In the case of thepsychological considerations, the smooth surface effectively meets theadage of out of sight out of mind such that a passenger is not remindedof the possibility of deployment of an air bag unit. The interior designconsideration enables smooth flowing surfaces to be incorporated in thecover material of an instrument panel on the passenger side thereof.

U.S. Pat. No. 3,640,546, issued Feb. 1, 1972 to D. S. Brawn, includes acover for a air bag unit having two doors that are covered by an outerlayer of material that is weakened along a joint line by reducing thethickness of the outer layer. Such thin sectioned seam lines can cause aresultant depression over time that will essentially outline the outletfrom the canister for the air bag component of the air bag unit. Thearrangement does not solve either the psychological awareness problem orthe problem of retaining a smooth, flowing surface appearance.

U.S. Pat. No. 4,246,213, issued Jan. 20, 1981 to Y. Takamatsu et al.,discloses a method for casting a V-shaped section at the tear seam.While the outer surface of the cover material is smooth the V-shapedconfiguration also reduces the thickness of the outer layer in anundesirable manner.

U.S. Pat. No. 5,082,310 discloses a cover for an air bag unit. The coverincludes two doors that are hinged for pivotal movement during air bagdeployment. The doors are covered by a layer of foam and the layer offoam is covered by an outer skin having a V-shape groove that is cut toweaken the skin.

One problem common to designs that cut or score a tear seam into anouter skin is that plastic materials especially, at cold temperatures,are prone to becoming brittle such that the cut or score line can inducecracking along the seam. At opposite temperature extremes typical skincover material such as thermoplastic olefins or thermoplastic polyvinylchloride become relatively soft and deformable such that they willstretch and remain unbroken during initial bag deployment. Anotherproblem that can arise with cut or scored tear seams is that they becomeobservable (read through outer surface) following extended periods ofexposure to heat and sunlight.

Another specific disadvantage of the cover shown in the '310 patent andanother cover shown in U.S. Pat. No. 4,886,630 is that they require thatthe outer skin be separately formed on a heated mold and then removedfrom the mold and cut before being co-molded to a foam layer in asubsequent molding operation.

The problems arising from separately forming a skin and then cutting thegrooves therein are obviated by the present method that employs castingtechniques disclosed in U.S. Pat. No. 4,623,503, issued Nov. 18, 1986 toE. Anetis et al., U.S. Pat. No. 4,562,025, issued Dec. 31, 1985 to JohnD. Gray and U.S. Pat. No. 4,925,151 issued May 15, 1990 to John D. Grayall of which are commonly assigned to the assignee of the presentinvention and each of which is hereby incorporated by reference.

SUMMARY OF THE INVENTION

The present invention is directed to a cover assembly for an air bagunit. The cover assembly has a skin or a shell with a tear seam thereinhaving a desired configuration such as the C, H, U, and X patternscommonly used to form tear patterns in the skin that will open duringair bag deployment to form an opening through which the air bag willpass as it inflates to protect an occupant of the vehicle. In particularthe skin or shell is formed of a first thermoplastic material having apredetermined thickness and a cast opening therein that has aconfiguration corresponding to a desired tear seam configuration andwherein the cast opening is filled with a second thermoplastic materialto form an integrally bonded filler strip in the skin or shell buthaving tensile and elongation properties less than that of the firstthermoplastic material that forms the skin or cover material such thatthe tear seam will not be elongated as much as the skin or shell athigher temperatures but will have sufficient compliance at lowertemperatures to prevent cracking at the tear seam. This invention alsocontemplates the use of filler strip materials having other differentproperties, e.g. lesser shear strength, flexural strength, burststrength, etc.

An apparatus for forming the skin or shell for the cover assemblyincludes a heatable mold. A powder box carries a seal gasket that isshaped to correspond to the shape of the desired tear seamconfiguration. The powder box and seal gasket thereon is adapted to beconnected to the heatable mold and to contain thermoplastic materialsuch as thermoplastic olefins or thermoplastic material such aspolyvinyl chloride (PVC) such as the pigmented particles or powderset-forth in U.S. Pat. No. 4,784,911 also commonly assigned to theassignee of the present invention and also incorporated herein byreference. The gasket pattern is arranged to impress against the surfaceof the heatable mold during the casting process and to leave a sealedfootprint thereon that corresponds to the shape of the desired tear seamconfiguration.

When the heatable mold is connected to the powder box, the gasket sealsthe mold surface such that following casting and curing of the skin orshell an opening is formed therein around the perimeter of the gaskethaving the same pattern as the tear seam. In order to produce the coverof the present invention the opening is then filled with thermoplasticmaterial having different tensile and elongation properties than that ofthe originally cast material so as to form a filler strip of materialthat will separate on air bag deployment to form an opening throughwhich the air bag can pass immediately upon vehicle impact.Additionally, the filler strip blends with the remainder of the skin orshell such that the cover assembly for the air bag unit has a smoothouter surface that hides the underlying air bag unit.

Accordingly, an object of the present invention is to provide an easilyassembled low cost outer skin or shell for use in a cover assembly foran air bag unit deployable into the passenger compartment of a motorvehicle wherein the outer skin has a preformed opening therein of thesame thickness as the remainder of the outer skin but conforming to adesired tear seam configuration established by an end user and whereinthe opening is filled to form an integrally bonded filler strip thatcombines with the outer skin to define a smooth, uninterrupted outersurface extending across both the preformed opening and the remainder ofthe outer skin.

A feature of the present invention is to provide such a low cost outerskin having a filler strip of a thermoplastic material that fills thepreformed opening and wherein the filler strip is integrally molded withthe remainder of the outer skin.

Another feature of the present invention is to provide a filler strip ofthermoplastic material that fills the preformed opening having tensileand elongation properties different than such properties of the materialforming the surrounding material of the outer skin.

Still another feature of the present invention is to provide such a lowcost outer skin having a cast thermoplastic outer skin with a preformedopening therein conforming to a desired tear seam configuration and afiller strip of a second thermoplastic material that fills the preformedopening to form a smooth uninterrupted outer surface on the outer skin.

Another object of the present invention is to provide an improvedapparatus for manufacturing the low cost outer skin of the presentinvention including: a heatable mold member, a powder box and a gasketconnected to the powder box that has a configuration that corresponds tothe shape of a desired seam configuration for a cover assembly thathides an underlying air bag unit and wherein the gasket further ismounted to engage a surface portion of the interior of the heatable moldmember to form a sealed footprint on the surface portion around which athermoplastic material is cast to form an outer skin with a preformedopening therein corresponding to the shape of a desired seamconfiguration.

Still another object of the invention is to provide a method for forminga weakened tear seam in the cover for an air bag unit comprising thesteps of sealing along a footprint corresponding to a tear seam, forminga preformed opening corresponding to a tear seam pattern in a firstthermoplastic material, and filling the preformed opening with a secondthermoplastic material having different tensile and elongationproperties than those of the first material.

These and other objects, features and advantages of the presentinvention and a more complete understanding thereof will be apparent tothose skilled in the art from the succeeding detailed description of theinvention and the accompanying drawings thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the present invention willhereinafter be described in conjunction with the appended drawings,wherein like designations denote like elements, and:

FIG. 1 is a perspective view of an automobile interior trim structureincorporating a tear seam of the present invention made from theapparatus of the present invention;

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1looking in the direction of the arrows;

FIG. 3 is an enlarged cross-sectional view of the structure of FIG. 2showing the detail of a preformed opening and filler strip componentsthereof;

FIG. 4 is a partial perspective view of an instrument panel mountedwithin an automobile interior compartment and showing in hidden lines atear seam of the present invention overlying an air bag deploymentcover;

FIG. 5 is a partial perspective view of the instrument panel of FIG. 4with the air bag deployment cover in an open position and with the tearseams therein separated;

FIG. 6 is a fragmentary top elevational view of the shell tool followingcasting of a first thermoplastic material around the gasket footprintand following separation of the shell tool from the powder box and tearseam pattern gasket and showing a cast skin or shell having a preformedopening thereon corresponding to a desired tear seam configuration;

FIG. 7 is a diagrammatic view of a shell tool and powder box apparatusof the present invention having a tear seam pattern with gasket thereon;

FIG. 8 is a diagrammatic view showing the preformed opening being filledwhile the skin remains in the shell tool;

FIG. 9 is a fragmentary sectional view of apparatus used in practicinganother embodiment of the method of this invention in forming anotherembodiment of an outer skin for the cover assembly of the presentinvention as shown in FIG. 10; and

FIG. 10 is a fragmentary perspective view of the embodiment of the outerskin formed by the apparatus and method of FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENT

In accordance with a preferred embodiment of the invention in FIG. 7 anapparatus 10 is illustrated for manufacturing the outer skin and air bagdeployment cover assembly of the present invention. The apparatus 10includes a powder box 12 having a peripheral portion 14 adapted to beconnected to the peripheral portion 16 of a shell tool 18 by suitableclamps that join the peripheral portions in a known manner.

The powder box 12 has a tear seam pattern 20 connected thereto thatincludes two cross legs 22, 24 and a center portion 26 that form anH-shaped pattern. Each of the legs 22, 24 and the center portion extendbeyond the depth of the powder box and outwardly of the peripheralportion 14 of the powder box such that they will penetrate into theinterior of the shell tool 18 when the powder box 12 is clamped to theshell tool 18. Each of the legs 22, 24 and center portion 26 have agasket mounting surface 28 thereon on which is affixed a gasket 30.

The tear seam defining gasket 30 is shown in FIG. 7 as an H-shapedconfiguration with outside legs 31 joined by a center portion 33. Eachof the legs 31 has free ends 31a, 31b, respectively, laterally spacedfrom spaced sidewalls 18b and 18c of the shell mold 18. The gasket 30 isconformable to a flat surface region 32 on the inner surface 34 of theshell tool 18 such that it will bridge the distance between the mountingsurface 28 and the flat surface region 32 and form a sealed foot printon the flat surface region 32 at a sealable portion 32a of the undividedsurface. The sealable portion 32a, because of the illustratedconfiguration of the gasket 30, is located inboard of the spacedsidewalls 18b, 18c. The gasket 30 can, of course, have any shape desiredso long as it corresponds to the tear seam pattern.

The process for manufacturing the outer skin and cover assembly of thepresent invention includes initially locating the shell tool 18 in aninverted position as shown in FIG. 7 such that the inner surface 34faces downwardly. The shell tool 18 is mated to the powder box 12 thatcontains a powdered thermoplastic material. When the peripheral portions14, 16 are connected, the shell tool 18 and powder box 12 form a sealedmold chamber 36 defined by the inner surface 34 and the interior wallsof the powder box 12. The thermoplastic material can be a dry resinpowder material with suitable coloring and plasticizer content, such asdescribed in U.S. Pat. No. 4,923,657 issued May 8, 1990 to J. C.Gembinski et al. Shell tool, and is heated to a sufficient temperatureto cause approximately one millimeter of dry powder to attach and fuse.Mold apparatus 10 is then rotated as a unit 180 degrees to dump the drypowder against the surface 34. Since the inner surface is heated, alayer of the dry powder forms across the surface 34 and about the outerperipheral edge 30a of the gasket 30 and fuses to form a skin 40 ofplastic with an H-shaped gap or opening 40a therein at the foot print ofthe gasket 30. The remaining powder is dumped back into the powder boxby rotating the mold apparatus 10 as a unit back to the initial positionshown in FIG. 6. The powder box 12 and shell tool 18 are thendisconnected and the shell tool 18 is heated more to cure thethermoplastic layer. Thereafter a second type of thermoplastic materialis deposited within the H-shaped gap or opening 40a while the skin 40 isin the shell tool 10 (FIG. 8). The shell tool 18 is heated to suitablycure both the originally deposited material that makes up the skin 40and the second deposited material that makes up a filler strip 40b thatfills the gap 40a. Finally, the shell tool 18 is cooled and the skin 40and H-configured filler strip formed integrally therewith are removed asa unit from the inner surface 34.

Automated production apparatuses for performing such steps are wellknown to those skilled in the art including U.S. Pat. No. 4,623,503,issued Nov. 18, 1986 to E. Anetis et al., U.S. Pat. No. 4,562,025,issued Dec. 31, 1985 to John D. Gray and U.S. Pat. No. 4,925,151 issuedMay 15, 1990 to John D. Gray. The manner of heating the shell tool 18will depend upon a particular operation but it is contemplated thatheating by directing a heated air stream on the outer surface 18a of theshell tool 18 will work. The gasket 30 cross-section can be a foamcompressible material such as a temperature resistant foam or it can bea hollow gasket either of the inflatable or non-inflatable type such asis shown in U.S. Pat. No. 4,925,151 issued May 15, 1990 to John D. Gray.

FIGS. 1-5 show an automobile interior trim structure 50 that includes acover assembly 52 for hiding an air bag unit 54 shown in outline brokenline form in FIG. 2. The cover assembly comprises an outer skin 56having a H-shaped filler strip 58 therein of an integrally moldedthermoplastic material having a lesser tensile strength than that ofsurrounding thermoplastic material of the outer skin 56. The coverassembly 52 has a smooth uninterrupted outer surface 60 that extendsacross the filler strip 58. Since the filler strip 58 is formed from adifferent type material than the remainder of the outer skin 56, a thinpaint coating 62 can be provided on the outer surface 60 to provide anidentical surface appearance. Alternatively, the filler strip materialand skin material can be blended to provide an identical appearancematch. In the illustrated embodiment the cover assembly 52 includes apair of doors 64, 66 formed as part of an insert 68 that forms anenclosure for an air bag canister 70 having a deployable air bag 72therein. The air bag 72 is inflated by a gas generator 74 upon ignitionin response to a signal from a controller 76 including collision sensingdevice 76a as is well known in the art. The configuration of the air bagunit and the arrangement of the components thereof will depend upon aparticular application and form no part of the present invention.Furthermore, the cover assembly 52 can be formed to have a single dooror other configuration that will spread open to bear against the outerskin 56 so as to cause separation thereof at the filler strip 58 thatdefines a lesser strength region in the outer skin 56 that willimmediately separate upon air bag deployment. In the illustratedembodiment, the filler strip 58 forms an H-shaped tear seam within theouter skin 56. The doors 64, 66 will pivot about hinges 64a, 66a asshown in FIG. 3 to press through a foam layer 78 located between theinsert 68 and the outer skin 56. The doors 64, 66 will act on the lesserstrength region defined by the filler strip 58 to produce an immediateseparation of the outer skin 56 to form an opening 80 as shown in FIG. 5such that the air bag 72 will be free to deploy into the passengercompartment immediately following a collision that will ignite the gasgenerator 74 and inflate the air bag 72 for deployment through theopening 80 formed by the separation of the H-shaped tear seam.

In accordance with the invention the H-shaped tear seam has a surfacesmoothness like that of the surrounding regions of the outer skin suchthat the cover assembly 52 will appear as a continuous uninterruptedsurface overlying the outlet from the canister that houses the air bag.It will of course be understood that the filler strip 58 that forms thelesser strength material region within the outer skin 56 can be shapedin other ways including C, U or X shapes as illustrated in co-pendingU.S. patent application Ser. No. 680,837 filed Apr. 5, 1991 and commonlyassigned with the present application. In one embodiment, the materialof lesser strength is a spray deposited highly glass filled or carbonateor other filler filled thermoplastic PVC or polyolefin material and thesurrounding material of the outer skin 56 is a thermoplastic materialformed from PVC. The lesser strength material that forms the fillerstrip 58 has a lower tensile and elongation property in the operationaltemperature range than that of the material comprising the remainder ofthe outer skin that is integrally bonded to and in surroundingrelationship to the periphery of the filler strip 58. Typically, theoperational temperature range in an instrument panel can range from -30°C. to 104° C.

The outer skin 56 provides a tear seam at the filler strip 58 that hasthe necessary thickness to hide any tendency to read through thelocation of the doors or the outlet from the canister. Nevertheless, thefiller strip 58 defines a tear seam that will provide an weak link atwhich the outer skin 56 will be easily separated.

In some cases, the need for a hidden seam line is less critical. If so,the method will include providing a nickel alloy mold shell 82 having astyling line protrusion 84 therein. As shown in FIG. 9, the sealinggasket 86 is positioned over the protrusion 84 to form a sealedfootprint corresponding to a desired tear seam pattern. The firstthermoplastic material is cast as layer 90. The gasket 86 is removed anda preformed opening 88 in layer 90 is then filled by casting, sprayingor otherwise depositing a second layer of thermoplastic material ofdesired, different properties than of the first material. A resultantrecessed styling filler strip 92 is formed on the layer 90 as shown inFIG. 10.

It will be appreciated from the foregoing description that the presentinvention not only includes an outer skin configuration that will assurecover assembly opening immediately upon vehicle collision butadditionally a outer skin configuration that will hide an underlying airbag unit over long periods of time. Furthermore, the arrangement willprotect an underlying air bag unit against either accidental orintentional tampering since there is no structure or door that can bepried open or inadvertently depressed into the structure of the air bagunit. It will be further appreciated by those skilled in the art thatthe foregoing description is for a preferred exemplary embodiment of theinvention and that the invention is not limited to the specificembodiments or material selections shown or discussed. For instance, inthe broader aspect of the outer skin, the seam forming gap can be filledwith a suitable bonding material with desired tensile strengthproperties so long as the gasket formed gap therein is filled to form asmooth outer surface and a thickness of material that will prevent readthrough of underlying air bag unit components. For instance, in thebroader aspect of the apparatus the gasket can be carried by a separatecarriage apart from a powder box such that the initial skin can beformed around a gasket footprint by spray deposit of the thermoplasticmaterial rather than rotational coating of the thermoplastic powder. Forinstance, in the broader aspect of the method, the initial coating withpreformed opening can be formed by an injection molding or a spray stepand the filling of the preformed opening can be accomplished by arotational deposition of thermoplastic material of lesser strength andlesser elongation under operating temperature conditions. In addition tothermoplastic PVC spray coatings, the method of the inventioncontemplates the use of spray coating urethane materials to either formthe preformed opening in the skin or shell or to form the filler strip.

Various changes and modifications will be apparent to those skilled inthe art and all such variations and modifications are intended to comewithin the spirit and scope of the appended claims.

What is claimed is:
 1. A thermoplastics casting mold assembly forforming an outer skin including an integral tear seam for a coverassembly for an air bag unit, the outer skin formed of a relativelystrong thermoplastic material and having a tear seam subsequently formedintegrally thereof of a relatively weak thermoplastic material with thetear seam corresponding to the general shape of a door or doors coveringthe outlet from a canister for the air bag in the air bag unit, the moldassembly comprising:a thin shell mold having spaced sidewalls and anundivided inner surface; an unsealed portion on said undivided innersurface for receiving a strong thermoplastic material castablethereagainst, a sealable portion on said undivided inner surface, saidsealable portion located inboard of said spaced sidewalls; a tear seamdefining gasket having a configuration including free ends laterallyspaced from said sidewalls of said shell mold; said configurationcorresponding generally to the shape and width of the tear seam; and atear seam pattern corresponding generally to the shape of said tear seamdefining gasket for holding said tear seam defining gasket against saidsealable portion of said undivided inner surface to form a sealed gasketfootprint on said undivided inner surface corresponding the exact shapeand width of the tear seam.
 2. The thermoplastics casting mold assemblyof claim 1, further comprising an unpartitioned powder box adapted to beconnected to said thin shell mold and including an inner surface thatcombines with the undivided inner surface of said thin shell mold toform a sealed chamber; said tear seam pattern connected to saidunpartitioned powder box and extending outwardly thereof and inwardly ofsaid thin shell mold to a point in close spaced relationship to saidsealable portion of said undivided inner surface of said thin shellmold; said tear seam defining gasket connected to said tear seam patternto bridge between said unpartitioned powder box and said sealableportion of said undivided inner surface to form said sealed gasketfootprint thereon.
 3. The thermoplastics casting mold assembly of claim1, wherein said tear seam defining gasket has a hollow section that isof greater depth when relaxed than when compressed against said sealableportion of said undivided inner surface to form the sealed gasketfootprint.
 4. The thermoplastics casting mold assembly of claim 2,wherein said tear seam defining gasket is compressed against saidsealable portion of said undivided inner surface to form the sealedgasket footprint on connection of said unpartitioned mold box to saidthin shell mold.
 5. The thermoplastics casting mold assembly of claim 4,wherein said tear seam defining gasket has a hollow section that is ofgreater depth when relaxed than when compressed against said sealableportion of said undivided inner surface to form the sealed gasketfootprint.
 6. The thermoplastics casting mold assembly of claim 1wherein said tear seam defining gasket has an H-shape.
 7. Thethermoplastics casting mold assembly of claim 1 wherein said tear seamdefining gasket has a C-shape.
 8. The thermoplastics casting moldassembly of claim 1 wherein said tear seam defining gasket has aU-shape.
 9. The thermoplastics casting mold assembly of claim 1 whereinsaid tear seam defining gasket has an X-shape.